1. Field of the Disclosure
This disclosure generally relates to an interactive input device and, more particularly, to a capacitive touch sensing system and an analog front end thereof.
2. Description of the Related Art
As the capacitive touch panel may achieve a better user experience, it has been broadly applied to various electronic devices such as a display device.
For example FIG. 1 shows a schematic block diagram of the conventional capacitive touch sensing system which includes a capacitive touch panel 91, a plurality of signal generators 92, a plurality of driving units 93, an analog front end 94, a digital back end 95 and a processing unit 96. The capacitive touch panel 91 includes a plurality of driving electrodes 911 intersecting with a plurality of sensing electrodes 912, wherein a mutual capacitance is formed between each of the driving electrodes 911 and each of the sensing electrodes 912. Each of the driving units 93 is coupled to one of the driving electrodes 911 for inputting a driving signal Sd generated by the associated signal generate 92. The sensing electrodes 912 output a sensing signal Ss, which is induced from the driving signal Sd through the mutual capacitance between the driving electrodes 911 and the sensing electrodes 912, to the analog front end 94. The analog front end 94 converts the sensing signal Ss to the digital signal which is then sent to the digital back end 95 for post-processing. The digital back end 95 is coupled to the processing unit 96 which identifies a touch position according to the post-processed result of the digital back end 95.
The analog front end 94 includes a plurality of amplification circuits 941, a plurality of anti-aliasing filters 942, an ADC buffer 943 and an AD converter 944, wherein the ADC buffer 943 is configured to buffer between the AD converter 944 and the anti-aliasing filters 942, and the anti-aliasing filters 942 are configured to reduce the signal noise outputted by the amplification circuits 941. In the above conventional technique, the sensing signal Ss is interfered by the electronic device in cooperation with the capacitive touch panel 91, e.g. the display device, to have high common mode noises. Generally speaking, as the touch signal outputted by the capacitive touch panel 91 is very small and in order to improve the identification ability of the touch signal in the environment with high common mode noises, the AD converter 944 having high resolution has to be employed. Meanwhile, in order to increase the signal-to-noise ratio, the oversampling technique is employed to sample the touch signal and as a high report rate has to be supported as well, the AD converter 944 has to operate at a high operating frequency. In addition, the anti-aliasing filters 942 and the ADC buffer 943 can increase the total chip area.
Accordingly, the present disclosure further provides a capacitive touch sensing system and an analog front end thereof that may decrease the required resolution and operating frequency of the AD converter and hence the power consumption as well as the chip area.